SAN FRANCISCO — Google said on Friday that for more than three years it had inadvertently collected snippets of private information that people send over unencrypted wireless networks.

The admission, made in an official blog post by Alan Eustace, Google’s engineering chief, comes a month after regulators in Europe started asking the search giant pointed questions about Street View, the layer of real-world photographs accessible from Google Maps. Regulators wanted to know what data Google collected as its camera-laden cars methodically trolled through neighborhoods, and what Google did with that data.

Google’s Street View misstep adds to the widespread anxiety about privacy in the digital age and the apparent willingness of Silicon Valley engineers to collect people’s private data without permission.

Facebook is currently engaged in a heated debate with its 400 million members about its shifting privacy guidelines, while Google has had to contend with other privacy missteps, like the introduction of its Buzz social network earlier this year that publicly exposed people’s closest e-mail contacts without permission.

Google appears to have acted quickly after questions were raised by the European regulators. Two weeks ago, Google tried to address their questions and criticism in a blog post. It said it did collect certain kinds of data around the world that identify Wi-Fi networks to help improve its mapping products. The information on wireless networks can be used for location-based advertising services for mobile phones, which can sometime be pinpointed via a wireless network even if they lack a GPS chip.

But the company explicitly said then that it did not collect or store so-called payload data — the actual information being transmitted by users over unprotected networks.

In a confession made on Friday afternoon (and late night, European time) that is sure to raise new questions about its privacy policies, Google said that its previous claims were wrong.

Mr. Eustace wrote that a review of the Street View software has revealed that because of a programming error in 2006, the company had indeed been mistakenly collecting snippets of data that happened to be transmitted over nonpassword protected Wi-Fi networks that the Google camera cars were passing. This occurred in Europe, in the United States and in other major cities elsewhere.

Mr. Eustace tried to play down the revelation, saying that Google “never used that data in any Google products.” He said that it collected only fragments of data, because the cars were moving constantly and changing channels many times each second. Only when someone was using their unencrypted, nonpassword-protected network was the data collected and stored.

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Google said it had temporarily halted its Street View cars and would stop collecting Wi-Fi network data entirely, Mr. Eustace wrote. He also said Google wanted to delete the data, in cooperation with regulators, as soon as possible.

But the revelation that the data was collected is likely to set off a firestorm of protest and possibly new legal problems. Google could be accused of intercepting private communications and violating wiretap laws in the United States, although it would most likely argue that it never had any intent to collect or use the data.

And in Europe, where Google has taken great pains to assure a queasy public about a giant American corporation taking photos of their neighborhoods, trust is likely to be further eroded.

Last month, Peter Schaar, Germany’s federal commissioner for data protection, said he was “horrified” by the earlier revelation that Google was collecting data about the location of Wi-Fi networks. He called on the company to “delete previously unlawfully collected personal data on the wireless network immediately and stop the rides for Street View.” Mr. Schaar could not be reached for further comment last night.

German data protection officials had initially questioned the legality of Street View but dropped their objections last July after Google agreed to hide details of faces, license plates and house numbers through pixilation, and to give citizens the option of removing their property entirely from the 360-degree photo archive. Since then, hundreds have made such requests. Some German politicians have advocated laws that would levy fines on companies that do not remove the information.

Marc Rotenberg, executive director of the Electronic Privacy Information Center in Washington, said that Friday’s news would “give quite a bit of ammunition to not only the European privacy commission but the European public, which has been very uneasy about Street View, far more than in the U.S.”

In the blog post, Mr. Eustace said of the Google engineering team: “We are profoundly sorry for this error and are determined to learn all the lessons we can from our mistake.”

A version of this article appears in print on May 15, 2010, on Page B1 of the New York edition with the headline: Google Says It Collected Private Data By Mistake. Order Reprints|Today's Paper|Subscribe